Wireless IC device, clip-shaped RFID tag, and article having RFID tag

ABSTRACT

In a wireless IC device, a columnar body includes a metal body with an insulating film. A loop-shaped antenna conductor is provided on an upper surface of the columnar body via an insulating pedestal. The loop surface of the antenna conductor is parallel or substantially parallel to the upper surface of the columnar body. On the lower surface of a RFIC element, two terminal electrodes are provided. The RFIC element is mounted on the antenna conductor such that the two terminal electrodes are connected to both ends of the antenna conductor, respectively. One end of the connecting conductor is connected to the vicinity of one end of the antenna conductor, and the other end of the connecting conductor is connected to the upper surface of the columnar body.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese Patent Application No. 2014-092643 filed on Apr. 28, 2014, Japanese Patent Application No. 2014-126813 filed on Jun. 20, 2014 and Japanese Patent Application No. 2014-222167 filed on Oct. 31, 2014 and is a Continuation Application of PCT Application No. PCT/JP2015/062030 filed on Apr. 21, 2015. The entire contents of each application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a wireless IC device and to a wireless IC device in which an RFIC (radio frequency integrated circuit) element is mounted on an object including a metal body. The present invention also relates to a clip-shaped RFID (radio frequency identifier) tag and to a clip-shaped RFID tag attachable to and detachable from a conductor of an article. The present invention further relates to an article including an RFID tag such as an article including a conductor and a clip-shaped RFID tag attachable to and detachable from the conductor.

2. Description of the Related Art

If an RFID tag utilizing the UHF band for wireless communications is directly affixed to a metal body, an electric field component of radio waves transmitted from a reader/writer becomes zero on a surface of the tag, making it unable to perform read/write of the tag. Therefore, when an RFID tag is affixed to a metal body, the RFID tag is generally located away from a metal surface.

In this regard, WO 2009/008296 discloses a technique of affixing an RFID tag having a loop antenna with a loop surface thereof perpendicular to a metal surface. This technique enables the RFID tag not only to pick up radio waves but also to utilize the metal surface as a radiation element, so that the RFID tag (wireless IC device) with a large gain is achieved.

According to JP 2004-192287 A, electronic data is stored in a clip clipping a medium to be clipped such as paper. The electronic data is output and input through wireless communications utilizing an RFID. According to JP 2004-307209 A, a notification assisting apparatus includes a first antenna part connected to a receiver, a second antenna part connected to an IC chip reader, and a clip-shaped main body to which these antenna parts are attached. When the notification assisting apparatus is attached to a file and the second antenna part is pivoted, the second antenna part projects downward from the notification assisting apparatus and comes into contact with, or in proximity to, a portion of the file. Transmission and reception between the notification assisting apparatus and an IC chip are smoothly performed through the second antenna part.

However, the structure of WO 2009/008296 including an RFID tag affixed with a loop surface perpendicular to a metal surface causes the RFID tag to project from the metal body and therefore is not suitable for a use particularly requiring robustness of a tag (e.g., for a gas cylinder).

By attaching an RFID tag to a clip as described in JP 2004-192287 A or JP 2004-307209 A the RFID tag can easily be attached to and detached from an object such as a paper document. However, if the object is a conductor, i.e., if the clip is attached to a conductor, the technique of JP 2004-192287 A or JP 2004-307209 A has a problem of not being able to ensure a sufficient communication distance because the conductor impairs the communication characteristics (particularly, the gain) of the RFID tag.

SUMMARY OF THE INVENTION

Therefore, preferred embodiments of the present invention provide wireless IC devices capable of enhancing the robustness and the gain.

Other preferred embodiments of the present invention provide clip-shaped RFID tags and articles including an RFID tag capable of enhancing the communication characteristics.

A wireless IC device according to a preferred embodiment of the present invention includes an object with a metal body; a loop conductor including a first loop end and a second loop end; an RFIC element including a first terminal electrode and a second terminal electrode respectively connected to the first loop end and the second loop end; and a connection conductor including a first end and a second end respectively connected to the loop conductor and the object, the first end is connected to the loop conductor in the vicinity of the first loop end.

Preferably, the loop conductor is disposed such that a loop surface of the lop conductor extends along a surface of the object.

Preferably, the RFIC element includes an RFIC chip including a first input/output terminal and a second input/output terminal respectively connected to the first terminal electrode and the second terminal electrode; an electrical length between the first input/output terminal and the second input/output terminal is about ½ of a wavelength of a communication signal; and an electrical length from a farthest end of the metal body based on the second end to the first input/output terminal is equal to or greater than about ½ of a wavelength of the communication signal.

In a certain aspect of a preferred embodiment of the present invention, the metal body includes a first edge that is different from a second edge corresponding to the farthest end, and the second end is connected at the first edge to the object.

In another aspect of a preferred embodiment of the present invention, the RFIC element further includes a power feeding circuit located between the loop conductor and the RFIC chip, and the first terminal electrode and the second terminal electrode are connected through the power feeding circuit to the first input/output terminal and the second input/output terminal.

Preferably, the wireless IC device further includes an insulator provided on the surface of the object, and the second end is connected through the insulator to the object.

A clip-shaped RFID tag according to a preferred embodiment of the present invention is a clip-shaped RFID tag attachable to and detachable from a conductor of an article, including a conductive clip attachable to the conductor; a loop conductor including a first loop end and a second loop end; an RFIC element including a first terminal electrode and a second terminal electrode respectively connected to the first loop end and the second loop end; and a connection conductor including a first end connected to the clip and a second end connected to the loop conductor in the vicinity of the first loop end.

Preferably, the first end of the connection conductor is connected to the clip at a position opposite to a point of action of the clip relative to a fulcrum of the clip.

Preferably, the RFIC element includes an RFIC chip including a first input/output terminal and a second input/output terminal respectively connected to the first terminal electrode and the second terminal electrode; an electrical length between the first input/output terminal and the second input/output terminal is about ½ of a wavelength of a communication signal; and an electrical length from a tip of the clip to the first input/output terminal is less than about ½ of a wavelength of the communication signal.

An article including an RFID tag according to a preferred embodiment of the present invention includes an article including a conductor; and a clip-shaped RFID tag attachable to and detachable from the conductor, the clip-shaped RFID tag including a conductive clip attached to the conductor, a loop conductor including a first loop end and a second loop end, an RFIC element including a first terminal electrode and a second terminal electrode respectively connected to the first loop end and the second loop end, and a connection conductor including a first end connected to the clip and a second end connected to the loop conductor in the vicinity of the first loop end.

A current flowing through the loop conductor is maximized in the vicinity of a loop end. Therefore, when the loop conductor and the object are connected, connecting the connection conductor in the vicinity of the loop end maximizes the current flowing through the metal body of the object and therefore improves the gain. By disposing the loop conductor on the object such that the loop surface is along the surface of the object, the robustness of the wireless IC device is improved.

A current amount (current density) flowing through the loop conductor is maximized in the vicinity of a loop end. Therefore, when the loop conductor and the clip is connected, connecting the connection conductor in the vicinity of the loop end maximizes the current amount flowing through the clip and therefore maximizes the current amount flowing through the conductor of the article to which the clip is attached. The conductor of the article defines and functions as a radiator or a radiation element, so that a high gain is produced. As a result, the communication characteristics are improved.

The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a basic configuration of a preferred embodiment of the present invention.

FIG. 2 is a perspective view of an example of a wireless IC device of a first preferred embodiment of the present invention viewed obliquely from above.

FIG. 3 is a top view of the wireless IC device of the first preferred embodiment of the present invention viewed from directly above.

FIG. 4 is a schematic of a connected state between an end of a connection conductor and a columnar body.

FIG. 5 is a schematic of an example of a structure of an RFIC element applied to the wireless IC device of the first preferred embodiment of the present invention.

FIG. 6 is a circuit diagram of an equivalent circuit of the wireless IC device of the first preferred embodiment of the present invention.

FIG. 7 is a circuit diagram of an equivalent circuit of the wireless IC device of a modification example of the first preferred embodiment of the present invention.

FIG. 8 is a perspective view of an example of a wireless IC device of a second preferred embodiment of the present invention viewed obliquely from above.

FIG. 9 is an exploded perspective view of an antenna conductor and an RFIC element mounted thereon.

FIG. 10 is a schematic of a connected state between the antenna conductor and a columnar body.

FIG. 11A is a schematic view of a portion of a process of producing the antenna conductor, FIG. 11B is a schematic view of another portion of the process of producing the antenna conductor, FIG. 11C is a schematic view of yet another portion of the process of producing the antenna conductor, and FIG. 11D is a schematic view of a further portion of the process of mounting an RFIC chip on the antenna conductor.

FIG. 12A is a top view of a clip-shaped RFID tag of a third preferred embodiment of the present invention viewed from directly above and FIG. 12B is a side view of the clip-shaped RFID tag of the third preferred embodiment of the present invention from the side.

FIG. 13 is a schematic of a connected state between a loop conductor and a connection conductor applied to the clip-shaped RFID tag of the third preferred embodiment of the present invention.

FIG. 14 is a schematic of a connected state between an RFIC element and the loop conductor applied to the clip-shaped RFID tag of the third preferred embodiment of the present invention.

FIG. 15 is a cross-sectional view of a structure of the RFIC element applied to the clip-shaped RFID tag of the third preferred embodiment of the present invention.

FIG. 16 is a circuit diagram of an equivalent circuit of the RFIC element applied to the clip-shaped RFID tag of the third preferred embodiment of the present invention.

FIG. 17A is a top view of the clip-shaped RFID tag of the third preferred embodiment of the present invention and a tray to which the clip-shaped RFID tag is attached viewed from directly above and FIG. 17B is a side view of the clip-shaped RFID tag of the third preferred embodiment of the present invention and the tray to which the clip-shaped RFID tag is attached viewed from the side.

FIG. 18 is a front view of the clip-shaped RFID tag of the third preferred embodiment of the present invention and a binder notebook to which the clip-shaped RFID tag is attached viewed from the front.

FIG. 19 is a perspective view of a binder clip when viewed obliquely.

FIG. 20 is a perspective view of a bulldog clip when viewed obliquely.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a wireless IC device 1 according to a preferred embodiment of the present invention preferably is an RFID device using the UHF band as a communication frequency. The wireless IC device 1 includes a loop conductor 2, an RFIC element 3, a connection conductor 4, and a metal body 5. The metal body 5 preferably has a rectangular or substantially rectangular columnar shape. The loop conductor 2, the RFIC element 3, and the connection conductor 4 are disposed on an upper surface of the metal body 5.

Specifically, the loop conductor 2 is disposed in a posture with a loop surface thereof parallel or substantially parallel to the upper surface of the metal body 5 at a slight distance from the upper surface of the metal body 5. In other words, the loop conductor 2 is disposed in a posture with the loop surface extending along the upper surface of the metal body 5 without contacting with the metal body 5 above the metal body 5.

An RFIC chip (not shown) includes a first input/output terminal and a second input/output terminal, and the RFIC is embedded inside the RFIC element 3. A lower surface of the RFIC element 3 is provided with a first terminal electrode and a second terminal electrode (both not shown) respectively connected to the first input/output terminal and the second input/output terminal. The first terminal electrode is connected to one end (a first loop end) 201 of the loop conductor 2, and the second terminal electrode is connected to the other end (a second loop end) 202 of the loop conductor 2. One end (a first end) 401 of the connection conductor 4 is connected to the vicinity of the one end 201 of the loop conductor 2, and the other end (a second end) 402 of the connection conductor 4 is connected to a predetermined position (certain edge) on the upper surface of the metal body 5.

With regard to the “vicinity” described above, when a length (an electrical length) from the one end 201 to the other end 202 of the loop conductor 2 is A, the connection conductor 4 is preferably connected to the loop conductor 2 within a range of length from the one end 201 up to approximately A/4, more preferably within a range of length from the one end 201 up to approximately A/8, for example.

An electrical length between the first input/output terminal and the second input/output terminal disposed on the RFIC chip is adjusted to about λ/2. The height of the metal body 5 (distance from the upper surface to the lower surface) is adjusted to about λ/2 or more. Since the other end 402 of the connection conductor 4 is connected to the predetermined position on the upper surface of the metal body 5, an electrical length from a farthest end of the metal body 5 based on the predetermined position to the first input/output terminal is also about λ/2 or more.

When a radio-frequency signal is transmitted from the RFIC element 3, a current I flows through the loop conductor 2 in a λ/4 mode, and a current I′ originated from the current I flows through the metal body 5 in a λ/2 mode. Therefore, the loop conductor 2 defines and functions as an exciter or an exciting loop, and the metal body 5 defines and functions as a radiator.

The one end 401 of the connection conductor 4 is connected to a point at which the current I flowing through the loop conductor 2 is maximized. As a result, the current I′ flowing through the metal body 5 is also maximized and, therefore, the radio-frequency transmission performance is improved (the gain for the wireless IC device is significantly improved). The loop surface of the loop conductor 2 is parallel or substantially parallel to the upper surface of the metal body 5. Therefore, the loop conductor 2 does not significantly project from the upper surface of the metal body 5 and the wireless IC device 1 is able to be enhanced in robustness.

First Preferred Embodiment

Referring to FIGS. 2 and 3, a wireless IC device 10 of a first preferred embodiment of the present invention includes a loop-shaped antenna conductor 12, a rectangular or substantially rectangular parallelepiped RFIC element 14, a belt-shaped connection conductor 16, an insulating pedestal (spacer) 18 defining a flat plate, and a rectangular or substantially rectangular columnar body 20. In the first preferred embodiment, an X-axis, a Y-axis, and a Z-axis are assigned to a width direction, a depth direction, and a height direction, respectively, of the columnar body 20.

The pedestal 18 includes a principal surface smaller than an upper surface of the columnar body 20 and is placed in a posture with the principal surface perpendicular or substantially perpendicular to the Z-axis on the center of the upper surface of the columnar body 20. The antenna conductor 12 has a loop surface smaller than the principal surface of the pedestal 18 and is placed in a posture with the loop surface perpendicular or substantially perpendicular to the Z-axis on the center of one principal surface (an upper surface) of the pedestal 18. Therefore, the antenna conductor 12 is disposed in a posture with the loop surface parallel or substantially parallel to the upper surface of the columnar body 20 (in a posture with the loop surface extending along the upper surface of the columnar body 20) at a position away from the columnar body 20. The RFIC element 14 is smaller than the antenna conductor 12 and is mounted on the antenna conductor 12 to straddle one end (a first loop end) 1201 and the other end (a second loop end) 1202 of the antenna conductor 12.

As can be seen from FIG. 5, the RFIC element 14 includes an RFIC chip 14 e processing an RFID signal and a power feeding circuit board 14 c on which the RFIC chip 14 e is mounted. The power feeding circuit board 14 c is made of ceramic or resin and has a plate shape. The RFIC chip 14 e includes a memory circuit and a signal processing circuit built-in and is sealed by a resin sealing layer 14 d. The side surfaces of the power feeding circuit board 14 c are perpendicular or substantially perpendicular to either the X-axis or Y-axis, and the side surfaces of the sealing layer 14 d are flush with the side surfaces of the power feeding circuit board 14 c.

A lower surface of the RFIC element 14 is provided with terminal electrodes 14 a and 14 b (14 a: a first terminal electrode, 14 b: a second terminal electrode) arranged along the X-axis. The terminal electrode 14 a is connected or bonded via a conductive bonding material 24 a (made of solder etc.) to the one end 1201 of the antenna conductor 12, and the terminal electrode 14 b is connected or bonded via a conductive bonding material 24 b (made of solder etc.) to the other end 1202 of the antenna conductor 12.

Input/output terminals 14 f and 14 g are provided on an upper surface of the power feeding circuit board 14 c. Input/output terminals 14 h and 14 i (14 h: a first input/output terminal, 14 i: a second input/output terminal) are provided on a lower surface of the RFIC chip 14 e. The input/output terminals 14 f and 14 g are connected or bonded by conductive bonding materials not shown (made of Ag etc.) to the input/output terminals 14 h and 14 i, respectively. The input/output terminals 14 h and 14 i are connected via a power feeding circuit 14 fct (see FIG. 6) disposed on the power feeding circuit board 14 c to the terminal electrodes 14 a and 14 b, respectively.

One end (a first end) 1601 of the connection conductor 16 is connected to the vicinity of the one end 1201 of the antenna conductor 12, and the other end (a second end) 1602 of the connection conductor 16 is connected to a predetermined position (certain edge) on the upper surface of the columnar body 20. Referring to FIG. 4, the columnar body 20 preferably includes a solid or hollow metal body 20 m and an insulation film 20 i covering the surface of the metal body 20 m. The one end 1601 of the connection conductor 16 is connected via a conductive bonding material such as solder to the antenna conductor 12, and the other end 1602 of the connection conductor 16 is bonded via an insulating bonding material 22 to the upper surface of the columnar body 20.

With regard to the “vicinity” described above, when a length (an electrical length) from the one end 1201 to the other end 1202 of the antenna conductor 12 is A, the connection conductor 16 is preferably connected to the antenna conductor 12 within a range of length from the one end 1201 up to approximately A/4, more preferably within a range of length from the one end 1201 up to approximately A/8, for example.

FIG. 6 shows an equivalent circuit of the wireless IC device 10. The power feeding circuit 14 fct is disposed on the power feeding circuit board 14 c. One end of a capacitor C1 is connected to the terminal electrode 14 a, and the other end of the capacitor C1 is connected to one end of an inductor L2. The other end of the inductor L2 is connected to the input/output terminal 14 f, and therefore, to the input/output terminal 14 h. One end of a capacitor C2 is connected to the terminal electrode 14 b, and the other end of the capacitor C1 is connected to the input/output terminal 14 g, and therefore, to the input/output terminal 14 i. One end of an inductor L1 is connected to the other end of the capacitor C1, and the other end of the inductor L1 is connected to the other end of the capacitor C2.

An inductor L0 is an inductor component of the antenna conductor 12 and is magnetically coupled to the inductors L1 and L2. A capacitor component based on the insulating bonding material 22 and the insulation film 20 i is present between the other end 1602 of the connection conductor 16 and the metal body 20 m. A capacitor C0 is this capacitor component. The inductor L0 and the capacitor C0 enable matching in a broadband.

An electrical length between the two input/output terminals 14 h and 14 i disposed on the RFIC chip 14 e is adjusted to about λ/2. The height of the metal body 20 m (distance from the upper surface to the lower surface) is adjusted to about λ/2 or more. Since the other end 1602 of the connection conductor 16 is connected to the predetermined position on the upper surface of the columnar body 20, an electrical length from a farthest end of the metal body 20 m based on the predetermined position to the input/output terminal 14 h is also about λ/2 or more.

When a radio-frequency signal is transmitted from the RFIC element 14, the current I′ originated from the current I flowing through the antenna conductor 12 flows through the columnar body 20. In this case, a maximum current point is formed at a position in the vicinity of the both ends 1201, 1202 of the antenna conductor 12, and a maximum voltage point is formed at a position in the vicinity of the center of the antenna conductor 12 (a position farthest from the RFIC element 14). Therefore, the antenna conductor 12 defines and functions as a first radiation element (an exciter or an exciting loop).

Since the other end 1602 of the connection conductor 16 is connected to the predetermined position on the upper surface of the columnar body 20 when the antenna conductor 12 and the columnar body 20 are connected, the current I′ tends to flow through the side surfaces of the metal body 20 m, and the columnar body 20 defines and functions as a second radiation element.

Additionally, since the one end 1601 of the connection conductor 16 is connected to the maximum current point of the antenna conductor 12, the current I′ flowing through the columnar body 20 is also maximized. As a result, the radio-frequency transmission performance is improved (the gain for the wireless IC device is significantly improved).

Since the loop surface of the antenna conductor 12 is parallel or substantially parallel to the upper surface of the columnar body 20, the antenna conductor 12 does not significantly project from the upper surface of the columnar body 20. As a result, the wireless IC device 10 is able to be enhanced in robustness.

Although the power feeding circuit 14 fct shown in FIG. 6 is disposed on the power feeding circuit board 14 c in the first preferred embodiment, the power feeding circuit 14 fct may not be included. In this case, the equivalent circuit is configured as shown in FIG. 7.

In the first preferred embodiment, the other end 1602 of the connection conductor 16 is bonded via the insulating bonding material 22 to the upper surface of the columnar body 20. However, the other end 1602 of the connection conductor 16 may directly be connected to the metal body 20 m.

In the first preferred embodiment, the RFIC element 14 has the structure in which the RFIC chip 14 e is sealed by the sealing layer 14 d so as to enhance the robustness. However, an RFIC bare chip may be configured as the RFIC element 14.

Second Preferred Embodiment

Referring to FIGS. 8 and 9, a wireless IC device 10 a of a second preferred embodiment of the present invention preferably includes an antenna conductor 32, the RFIC element 14, and a circular columnar body 30.

The antenna conductor 32 is a conductor including a loop portion (loop conductor) 321 p, a leg portion (portion of a connection conductor) 321 g, and a fixing portion (another portion of the connection conductor) 32 fx integrally formed. As described later in detail, the antenna conductor 32 is produced preferably by punching and bending of a hoop material. As a result, a principal surface of the loop portion 321 p and a principal surface of the fixing portion 32 fx spread in parallel or substantially in parallel with each other, and a principal surface of the leg portion 321 g extends perpendicularly or substantially perpendicularly to the principal surface of the loop portion 321 p or the fixing portion 32 fx.

The loop portion 321 p includes one end (a first loop end) 321 p 01 and the other end (a second loop end) 321 p 02 and defines a loop considerably smaller than an upper surface (=a cross section perpendicular or substantially perpendicular to the axis of the column) of the columnar body 30. In this case, a loop surface extends parallel or substantially parallel with the principal surface of the loop portion 321 p.

The one end 321 g 01 of the leg portion 321 g defines a first end of the connection conductor and is connected to the vicinity of the one end 321 p 01 of the loop portion 321 p. The other end 321 g 02 of the leg portion 321 g is connected to the fixing portion 32 fx. The fixing portion 32 fx also defines a loop, and the other end 321 g 02 of the leg portion 321 g is connected to one end of this loop. The other end (a second end of the connection conductor) 32 fx 01 of the loop drawn by the fixing portion 32 fx is connected to a predetermined position (certain edge) on the upper surface of the columnar body 30.

With regard to the “vicinity” described above, when a length (an electrical length) from the one end 321 p 01 to the other end 321 p 02 of the loop portion 321 p is A, the leg portion 321 g is preferably connected to the loop portion 321 p within a range of length from the one end 321 p 01 up to approximately A/4, more preferably within a range of length from the one end 321 p 01 up to approximately A/8, for example.

While the antenna conductor 32 is mounted on the upper surface of the columnar body 30 in this way, the principal surface of the fixing portion 32 fx extends parallel or substantially parallel with the upper surface of the columnar body 30. The principal surface of the loop portion 321 p extends parallel or substantially parallel with the principal surface of the fixing portion 32 fx, and the loop portion 321 p is connected via the leg portion 321 g to the fixing portion 32 fx. Therefore, the loop portion 321 p is disposed in a posture with the loop surface parallel to the upper surface of the columnar body 30 (in a posture with the loop surface extending along the upper surface of the columnar body 30) at a position at a predetermined interval from the columnar body 30.

The RFIC element 14 has the structure shown in FIG. 5 and is smaller than the loop portion 321 p and mounted on the loop portion 321 p to straddle the one end 321 p 01 and the other end 321 p 02 of the loop portion 321 p. The terminal electrodes 14 a and 14 b disposed on the RFIC element 14 are respectively connected or bonded via conductive bonding materials (not shown) such as solder to the one end 321 p 01 and the other end 321 p 02 of the loop portion 321 p.

Referring to FIG. 10, the columnar body 30 includes a solid or hollow metal body 30 m and an insulation film 30 i covering the surface of the metal body 30 m. The fixing portion 32 fx is bonded via an insulating bonding material 34 to the upper surface of the columnar body 30.

An electrical length between the two input/output terminals 14 h and 14 i disposed on the RFIC chip 14 e is adjusted to about λ/2. The height of the metal body 30 m (distance from the upper surface to the lower surface) is adjusted to about λ/2 or more. Since the loop portion 321 p is connected via the leg portion 321 g and the fixing portion 32 fx to the upper surface of the columnar body 30, an electrical length from a farthest end of the metal body 30 m based on the predetermined position of connection of the fixing portion 32 fx to the input/output terminal 14 h is also about λ/2 or more.

When a radio-frequency signal is transmitted from the RFIC element 14, the current I′ originated from the current I flowing through the loop portion 321 p flows through the columnar body 30. In this case, a maximum current point is formed at a position in the vicinity of the both ends 321 p 01, 321 p 02 of the loop portion 321 p, and a maximum voltage point is formed at a position in the vicinity of the center of the loop portion 321 p (a position farthest from the RFIC element 14). Therefore, the loop portion 321 p defines and functions as the first radiation element (an exciter or an exciting loop).

Since the other end 32 fx 02 of the fixing portion 32 fx connected via the leg portion 321 g to the loop portion 321 p is connected to the predetermined position on the upper surface of the columnar body 30, the current I′ tends to flow through the side surfaces of the metal body 30 m, and the columnar body 30 defines and functions as the second radiation element.

Additionally, since the one end 321 g 01 of the leg portion 321 g is connected to the maximum current point of the loop portion 321 p, the current I′ flowing through the columnar body 30 is also maximized. As a result, the radio-frequency transmission performance is improved (the gain for the wireless IC device is significantly improved).

Since the loop surface of the loop portion 321 p is parallel or substantially parallel to the upper surface of the columnar body 30, the loop portion 321 p does not significantly project from the upper surface of the columnar body 30. As a result, the wireless IC device 10 a is able to be enhanced in robustness.

A non-limiting example of a method of manufacturing the antenna conductor 32 and a method of mounting the RFIC element 14 will be described with reference to FIGS. 11A to 11D.

First, a plate-shaped conductor including the loop portion 321 p, the leg portion 321 g, and the fixing portion 32 fx is punched out from a hoop material (see FIG. 11A). The leg portion 321 g and the fixing portion 32 fx are then bent 90° downward at a connection portion between the loop portion 321 p and the leg portion 321 g (see FIG. 11B). Subsequently, the fixing portion 32 fx is bent 90° upward at a connection portion between the leg portion 321 g and the fixing portion 32 fx (see FIG. 11C). After the antenna conductor 32 is completed in this way, the RFIC element 14 is mounted to straddle the one end 321 p 01 and the other end 321 p 02 of the loop portion 321 p (see FIG. 11D).

As described above, the loop portion 321 p, the leg portion 321 g, and the fixing portion 32 fx of the antenna conductor 32 are preferably integrally formed by punching and bending of the hoop material. Therefore, the antenna conductor 32 is easily produced.

Third Preferred Embodiment

Referring to FIGS. 12A, 12B, 13, and 14, a clip-shaped RFID tag 100 of a third preferred embodiment of the present invention preferably is an RFID tag using the 900 MHz band as a communication frequency and includes a crocodile clip 120, a lead wire 140, an RFIC element 180, and a loop conductor 220.

The crocodile clip 120 includes conductive clip pieces 121 and 122. A serrated locking portion 121 t is provided on an inside surface of a tip of the clip piece 121, and a serrated locking portion 122 t is provided on an inside surface of a tip of the clip piece 122. The length of the clip piece 122 exceeds the length of the clip piece 121, and a retainer 124 (described later in detail) retaining the lead wire 140 is provided at a base end of the clip piece 122.

The clip pieces 121 and 122 are supported by a conductive shaft (supporting member) 123 such that the locking portions 121 t and 122 t engage with each other, and are made swingable in the rotation direction of the shaft 123. A torsion coil spring not shown is disposed around the shaft 123, and the locking portion 121 t of the clip piece 121 is pressed against the locking portion 122 t of the clip piece 122 by the restoring force of the torsion coil spring.

The crocodile clip 120 having such a structure allows the shaft 123 to define and function as a fulcrum, the tips of the clip pieces 121 and 122 to define and function as points of action, and the base ends of the clip pieces 121 and 122 to define and function as points of force. The locking portion 121 t of the clip piece 121 is separated from the locking portion 122 t of the clip piece 122 by applying to the points of effort an external force exceeding the restoring force of the torsion coil spring in the opposite direction.

The loop conductor 220 is a loop-shaped antenna conductor including a first loop end 2201 and a second loop end 2202 and is supported by an insulating base plate 200. The base plate 200 has a principal surface defining a rectangle, and the size of this rectangle is identical to the rectangle circumscribing the loop conductor 220 in a planar view.

The lead wire 140 includes a wire connection conductor (core wire) 142 and a resin 141 covering the connection conductor 142 except a first end 14201 and a second end 14202. A certain position of the lead wire 140 (a position closer to the first end 14201 as compared to the center of the resin 141 in the length direction) is engaged with the retainer 124 disposed at the base end of the clip piece 122. As a result, the lead wire 140 is retained by the crocodile clip 120.

The first end 14201 of the connection conductor 142 is connected to the clip piece 122 by a conductive bonding material 161 (made of solder etc.; the same shall apply hereinafter). The second end 14202 of the connection conductor 142 is connected to the loop conductor 220 by a conductive bonding material 162. More specifically, the first end 14201 of the connection conductor 142 is connected to the clip piece 122 at a position close to the retainer 124, i.e., a position opposite to the point of action of the crocodile clip 120 relative to the fulcrum of the crocodile clip 120. The second end 14202 of the connection conductor 142 is connected to the vicinity of the first loop end 22001 of the loop conductor 220.

With regard to the “vicinity,” when a length (an electrical length) from the first loop end 22001 to the second loop end 22002 of the loop conductor 220 is A, the connection conductor 142 is preferably connected to the loop conductor 220 within a range of length from the first loop end 22001 up to approximately A/4, more preferably within a range of length from the first loop end 22001 up to approximately A/8, for example.

Connecting the first end 14201 of the connection conductor 142 to the position described above reduces the risk of the connection conductor 142 preventing the attachment/detachment of the clip 120 and extends the electrical length from the tip of the clip piece 122 to the second end 14202 of the connection conductor 142 (described later in detail).

The RFIC element 180 is mounted on the loop conductor 220 to straddle the first loop end 22001 and the second loop end 22002. Specifically, the RFIC element 180 includes a first terminal electrode 180 a and a second terminal electrode 180 b, and the first terminal electrode 180 a is connected by a conductive bonding material 240 a to the first loop end 22001 while the second terminal electrode 180 b is connected by a conductive bonding material 240 b to the second loop end 22002.

As can be seen from FIG. 15, the RFIC element 180 preferably includes an RFIC chip 180 e processing an RFID signal and a power feeding circuit board 180 c on which the RFIC chip 180 e is mounted. The power feeding circuit board 180 c is made of ceramic or resin and preferably has a plate shape. The RFIC chip 180 e includes a memory circuit and a signal processing circuit built-in and is sealed by a resin sealing layer 180 d.

Input/output terminals 180 f and 180 g are provided on an upper surface of the power feeding circuit board 180 c. Input/output terminals 180 h and 180 i (180 h: a first input/output terminal, 180 i: a second input/output terminal) are provided on a lower surface of the RFIC chip 180 e. The input/output terminals 180 f and 180 g are connected by conductive bonding materials not shown (made of Ag etc.) to the input/output terminals 180 h and 180 i, respectively. The input/output terminals 180 f and 180 g are connected via a power feeding circuit 180 j (see FIG. 16) disposed on the power feeding circuit board 180 c to the first terminal electrode 180 a and the second terminal electrode 180 b, respectively.

FIG. 16 shows an equivalent circuit of the RFIC element 180. In the power feeding circuit 180 j, one end of a capacitor C11 is connected to the first terminal electrode 180 a, and the other end of the capacitor C11 is connected to one end of an inductor L11. The other end of the inductor L11 is connected to the input/output terminal 180 f, and therefore, to the input/output terminal 180 h. One end of a capacitor C12 is connected to the second terminal electrode 180 b, and the other end of the capacitor C12 is connected to the input/output terminal 180 g, and therefore, to the input/output terminal 180 i. One end of an inductor L12 is connected to the other end of the capacitor C11, and the other end of the inductor L12 is connected to the other end of the capacitor C12. The inductors L11 to L12 and the capacitors C11 to C12 enable matching in a broadband.

An electrical length between the input/output terminals 180 h and 180 i disposed on the RFIC chip 180 e is adjusted to about λ/2 (=½ wavelength of a communication signal). In contrast, an electrical length from the input/output terminal 180 h to the tip of the clip piece 122 is adjusted to a value less than about λ/2 (preferably, a value set as close as possible to about λ/2 without causing resonance).

The clip-shaped RFID tag 100 is attached to a conductive tray (article) 300 made of metal or carbon in a manner shown in FIGS. 17A and 17B. An electrical length from a farthest end of the tray 300 based on the attachment position (an end in an open state farthest from the attachment position) to the input/output terminal 180 h indicates a value of about λ/2 or more. If the clip-shaped RFID tag 100 is attached to a predetermined position of the tray 300, an electrical length from the farthest end of the tray 300 based on the predetermined position to the input/output terminal 180 h indicates an integer multiple of about λ/2.

When a radio-frequency signal is transmitted from the RFIC element 180, the current I′ originated from the current I flowing through the loop conductor 220 flows through the crocodile clip 120 and the tray 300. In this case, a maximum current point (a point of maximized current density) is formed at a position in the vicinity of the both ends 22001, 22002 of the loop conductor 220, and a maximum voltage point is formed at a position in the vicinity of the center of the loop conductor 220 (a position farthest from the RFIC element 180). Therefore, the loop conductor 220 defines and functions as an exciter or an exciting loop, and the crocodile clip 120 and the tray 300 define and function as radiators or radiation elements.

Additionally, since the second end 14202 of the connection conductor 142 is connected to the maximum current point of the loop conductor 220, the current I′ flowing through the crocodile clip 120 and the tray 300 is also maximized. As a result, the gain of the communication signal is significantly improved. In other words, an improvement is made in radio-frequency transmission performance or communication characteristics.

Since the electrical length from the input/output terminal 180 h to the tip of the clip piece 122 is adjusted to a value less than about λ/2, the gain of the communication signal is significantly reduced when the clip-shaped RFID tag 100 is removed from the tray 300. Therefore, a communication operation is able to be substantially turned on/off by attaching/detaching the clip-shaped RFID tag 100 to/from the tray 300.

In the third preferred embodiment, the clip-shaped RFID tag 100 is assumed to be attached to the conductive tray 300. However, a binder notebook 400 shown in FIG. 18 may be prepared as the article, and the clip-shaped RFID tag 100 may be attached to a helical metal fitting (conductor) 400 m disposed on the binder notebook 400. In this case, the length of the helix defining the metal fitting 400 m is adjusted to a length corresponding to an electrical length of about λ/2 or more. Therefore, when the clip-shaped RFID tag 100 is attached to the metal fitting 400 m, the metal fitting 400 m defines and functions as a radiator or a radiating element.

Although the metal fitting 400 m is assumed to be formed into a helical shape in FIG. 18, a plurality of metal fittings each defining a ring may be used instead of the helical metal fitting 400 m. In this case, the rings must be adjusted in size such that an electrical length from a farthest end of the rings to the input/output terminal 180 h becomes equal to or greater than about λ/2, for example.

Although the crocodile clip 120 is preferably used as the clip in the third preferred embodiment, a conductive binder clip or bulldog clip may be used instead (see FIGS. 19 and 20).

In the third preferred embodiment, the locking portions 121 t and 122 t of the crocodile clip 120 are directly connected to the conductor of the article. However, a non-slip member such as conductive rubber or insulating rubber may be attached to each of the locking portions 121 t and 122 t. Attachment of the non-slip members reduces the risk of the crocodile clip 120 easily dropping off from the article. If insulating rubber is used as the non-slip member, a capacitance is generated between the locking portion 121 t or 122 t and the article.

Although the power feeding circuit 180 j shown in FIG. 16 is disposed on the power feeding circuit board 180 c in the third preferred embodiment, the power feeding circuit 18 j may not be included. In the third preferred embodiment, the RFIC element 180 has the structure in which the RFIC chip 180 e is sealed by the sealing layer 180 d so as to enhance the robustness. However, an RFIC bare chip may be configured as the RFIC element 180.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

What is claimed is:
 1. A wireless IC device comprising: an object including a metal body; a loop conductor including a first loop end and a second loop end; an RFIC element including a first terminal electrode and a second terminal electrode respectively connected to the first loop end and the second loop end; and a connection conductor including a first end and a second end respectively connected to the loop conductor and the object; wherein a loop surface of the loop conductor extends along a surface of the object.
 2. The wireless IC device according to claim 1, wherein the RFIC element includes an RFIC chip including a first input/output terminal and a second input/output terminal respectively connected to the first terminal electrode and the second terminal electrode; an electrical length between the first input/output terminal and the second input/output terminal is about ½ of a wavelength of a communication signal; and an electrical length from a farthest end of the metal body based on the second end to the first input/output terminal is equal to or greater than about ½ of a wavelength of the communication signal.
 3. The wireless IC device according to claim 2, wherein the metal body includes a first edge different from a second edge corresponding to the farthest end of the metal body; and the second end is connected at the first edge to the object.
 4. The wireless IC device according to claim 2, wherein the RFIC element further includes a power feeding circuit located between the loop conductor and the RFIC chip; and the first terminal electrode and the second terminal electrode are connected through the power feeding circuit to the first input/output terminal and the second input/output terminal.
 5. The wireless IC device according to claim 1, further comprising an insulator on the surface of the object; wherein the second end is connected through the insulator to the object.
 6. The wireless IC device according to claim 1, wherein the loop conductor, the RFIC element, and the connection conductor are disposed on an upper surface of the metal body.
 7. The wireless IC device according to claim 1, wherein a length from the first loop end to the second loop end of the loop conductor is A, the connection conductor is connected to the loop conductor within a range of length from the first loop end up to approximately A/4.
 8. The wireless IC device according to claim 1, wherein a length from the first loop end to the second loop end of the loop conductor is A, the connection conductor is connected to the loop conductor within a range of length from the first loop end up to approximately A/8.
 9. The wireless IC device according to claim 1, wherein the RFIC element includes an RFIC chip and a power feeding circuit board.
 10. The wireless IC device according to claim 9, further comprising a sealing layer that seals the RFIC chip to the power feeding circuit board.
 11. The wireless IC device according to claim 1, wherein the loop conductor defines an antenna conductor that includes a leg portion and a fixing portion. 